Also, it's quite possible that the pregnancy would have happened anyway. People with such conditions do become pregnant, and if it happened directly after herbal treatment despite that treatment being ineffective, that's the very definition of coincidence.
"Some researchers believe that placebos simply evoke a psychological response. The act of taking them gives you an improved sense of well-being. However, recent research indicates that placebos may also bring about a physical response."
I think you're falling for the post hoc, ergo propter hoc, logical fallacy. Once case simply doesn't prove therapeutic value.
"Post hoc ergo propter hoc (Latin: "after this, therefore because of this") is a logical fallacy (of the questionable cause variety) that states "Since event Y followed event X, event Y must have been caused by event X." It is often shortened to simply post hoc. "